1. Field of the Invention
The present invention relates to the forming of capacitive elements in an integrated circuit. The present invention more specifically relates to the forming of capacitive elements based on perovskite oxides.
The invention applies, for example, to the forming of high-density memory integrated circuits in which the memory point capacitors are formed in a perovskite layer to form the dielectric.
2. Discussion of the Related Art
A difficulty of the use of perovskite oxides in the forming of semiconductor circuits is linked to the poor crystal growth of perovskites on silicon substrate. The thin perovskite layer or film deposited on a silicon substrate does not maintain the properties of the single crystal or of the ceramic. An interface must thus be interposed between the silicon substrate and this perovskite. The same problems are posed for the crystal growth of perovskites on a metal layer or on an amorphous oxide, which form the other types of layers above which it is generally desired to form integrated capacitors.
To maintain the single-crystal structure of the perovskite forming the dielectric of the capacitive elements, the interface on which this perovskite is deposited must enable deposition by epitaxy. Further, this interface must adhere in crystallized form on the underlying substrate and form a diffusion and reaction barrier between the silicon (oxidized or not) and the perovskite.
Among the perovskites generally used to form the dielectric layers deposited by epitaxy on silicon substrates, one can find:
barium strontium titanates (BST) having formula (Ba,Sr)TiO3;
lead zirconate titanates (PZT), of formula Pb(Zr,Ti)O3 and their derivatives such as, for example, lead lanthanum zirconate titanates (PLZT); and
double layer perovskites such as strontium bismuth tantalate (SBT) of formula SrBi2Ta2O9, or strontium bismuth niobate (SBN) of formula SrBi2Nb2O9.
To enable deposition of such perovskites on a silicon oxide substrate (SiO2), an interface formed of a BiT perovskite (Bi4Ti3O12) is generally used.
A disadvantage of using BiT as an interface is that it is an insulating perovskite. Accordingly, to form a capacitive element from an SiO2 substrate, the BiT must be covered with another conductive perovskite, for example, LSCO ((La,Sr)CoO3), before depositing the dielectric layer.
A disadvantage then is a complexity of the forming process and of the obtained structure.
An example of use of BiT as an interface for the epitaxy of a perovskite is described in the article: “Template Approaches to Growth of Oriented Oxide Heterostructures on SiO2/Si” by R. Ramesh et al. published in 1994 in “Journal of Electronic Materials”, Vol. 23, n° 1.